net: qualcomm: rmnet: use masks instead of C bit-fields

The actual layout of bits defined in C bit-fields (e.g. int foo : 3)
is implementation-defined.  Structures defined in <linux/if_rmnet.h>
address this by specifying all bit-fields twice, to cover two
possible layouts.

I think this pattern is repetitive and noisy, and I find the whole
notion of compiler "bitfield endianness" to be non-intuitive.

Stop using C bit-fields for the command/data flag and the pad length
fields in the rmnet_map structure, and define a single-byte flags
field instead.  Define a mask for the single-bit "command" flag,
and another mask for the encoded pad length.  The content of both
fields can be accessed using a simple bitwise AND operation.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 13 deletions

diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 8c7845baf383..a02f0a3df1d9 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -6,21 +6,18 @@
 #define _LINUX_IF_RMNET_H_
 
 struct rmnet_map_header {
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u8  pad_len:6;
-	u8  reserved_bit:1;
-	u8  cd_bit:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u8  cd_bit:1;
-	u8  reserved_bit:1;
-	u8  pad_len:6;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
-	u8  mux_id;
-	__be16 pkt_len;
+	u8 flags;			/* MAP_CMD_FLAG, MAP_PAD_LEN_MASK */
+	u8 mux_id;
+	__be16 pkt_len;			/* Length of packet, including pad */
 }  __aligned(1);
 
+/* rmnet_map_header flags field:
+ *  PAD_LEN:	number of pad bytes following packet data
+ *  CMD:	1 = packet contains a MAP command; 0 = packet contains data
+ */
+#define MAP_PAD_LEN_MASK		GENMASK(5, 0)
+#define MAP_CMD_FLAG			BIT(7)
+
 struct rmnet_map_dl_csum_trailer {
 	u8  reserved1;
 #if defined(__LITTLE_ENDIAN_BITFIELD)